HC05V7GRSSLASHD datasheet(129/170 Pages) NXP

129 / 170 page

SECTION 15: MESSAGE DATA LINK CONTROLLER

Page 115

MC68HC05V7 Specification Rev. 1.0

15.5.2.4

EOD - End of Data Symbol

The EOD symbol is a short passive period on the J1850 bus used to signify to any

recipients of a message that the transmission by the originator has completed.

15.5.2.5

IFR - In Frame Response Bytes

The IFR section of the J1850 message format is optional. The MDLC does not support this

option. The MDLC will not transmit an IFR under any circumstances. If an IFR is received

from another node, the MDLC will ignore this part of the message and wait for the EOF

symbol before resuming normal operation.

15.5.2.6

EOF - End of Frame Symbol

This symbol is a passive period on the J1850 bus, longer than an EOD symbol, which

signifies the end of a message. Since an EOF symbol is longer than an EOD symbol, if no

response is transmitted after an EOD symbol, it becomes an EOF, and the message is

assumed to be completed.

15.5.2.7

IFS - Inter-Frame Separation Symbol

The IFS symbol is a passive period on the J1850 bus that allows proper synchronization

between nodes during continuous message transmission. The IFS symbol is transmitted

by a node following the completion of the EOF period.

When the last byte of a message has been transmitted onto the J1850 bus, and the EOF

symbol time has expired, all nodes must then wait for the IFS symbol time to expire before

transmitting an SOF, marking the beginning of another message.

However, if the MDLC is waiting for the IFS period to expire before beginning a

transmission and a rising edge is detected before the IFS time has expired, it must

internally synchronize to that edge. If a write to the MTCR register (initiate transmission)

occurred on or before 104

· t

MDLC from the received rising edge, then the MDLC will transmit

and arbitrate for the bus. If a CPU write to the MTCR register occurred after 104

· tmdlc from

the detection of the rising edge, then the MDLC will not transmit, but will wait for the next

IFS period to expire before attempting to transmit the message.

A rising edge may occur during the IFS period because of varying clock tolerances and

loading of the J1850 bus, causing different nodes to observe the completion of the IFS

period at different times. Receivers must synchronize to any SOF occurring during an IFS

period to allow for individual clock tolerances.

15.5.2.8

BREAK - Break

Any MDLC transmitting at the time a BREAK is detected will treat the BREAK as if a loss

of arbitration had occurred, and halt transmission. The MDLC cannot transmit a BREAK

symbol. If while receiving a message the MDLC detects a BREAK symbol, it will treat the

BREAK as a reception error and clear any partially received message from the Rx buffer.

15.5.2.9

Idle Bus

An idle condition exists on the bus during any passive period after expiration of the IFS

period. Any node sensing an idle bus condition can begin transmission immediately.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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